Ankle-Foot Prosthesis for Automatic Adaptation to Sloped Walking Surfaces

ABSTRACT

An ankle-foot prosthesis includes a foot plate, an ankle frame attached to the foot plate, a yoke pivotally connected to the ankle frame and including a member for attaching to a leg, a damper having a first end connected to the yoke and a second end connected to the ankle frame, and a control mechanism for switching the damper between low and high settings.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. application Ser. No. 15/434,533, filed Feb. 16, 2017, which is a continuation-in-part (CIP) application of U.S. application Ser. No. 15/359,242, filed Nov. 22, 2016, now U.S. Pat. No. 10,105,243, which is a continuation application of U.S. application Ser. No. 14/022,645, filed Sep. 10, 2013, now U.S. Pat. No. 9,549,827, which claims priority based on prior two (2) U.S. Provisional Applications S.N. 61/703,799, filed Sep. 21, 2012, and Ser. No. 61/851,740, filed Mar. 13, 2013, all of which are hereby incorporated herein in their entirety by reference. The present application is further related to International Application No. PCT/US2007/022208, filed Oct. 17, 2007 (WO 2008/048658, Apr. 24, 2008) (U.S. application Ser. No. 12/311,818, filed Apr. 13, 2009, Published as US 2010/0185301, on Jul. 22, 2010), U.S. application Ser. No. 12/462,056, filed Jul. 28, 2009 (Published as US 2010/0030343, on Feb. 4, 2010), U.S. application Ser. No. 13/066,361, filed Apr. 12, 2011 (Published as US 2012/0016493, on Jan. 19, 2012), U.S. application Ser. No. 13/374,881, filed Jan. 20, 2012 (Published as US 2013/0006386, on Jan. 3, 2013), and International Application No. PCT/US2011/000675, filed Apr. 4, 2011 (WO 2011/129892, Oct. 20, 2011), all of which are hereby incorporated herein in their entirety by reference.

FIELD AND BACKGROUND OF THE INVENTION

The present invention is generally directed to prosthetic and orthotic devices, and more particularly to an ankle-foot prosthesis for automatic adaptation to level, as well as sloped walking surfaces. Even more particularly, the invention is directed to a device or system for use by lower limb amputees to more easily and safely walk over a variety of sloped terrain, as well as to provide more stability during standing and swaying tasks.

Most currently available prosthetic ankle devices are spring-like structures that operate about one equilibrium point (i.e., one resting angle). These systems can work nicely on level terrain but cause instabilities when lower limb prosthesis users walk on sloped surfaces. Many systems have been described that use hydraulic dampers and/or variations of damping to adjust the properties of the prosthesis (Mauch, 1958—U.S. Pat. No. 2,843,853; Koniuk, 2002—U.S. Pat. No. 6,443,993; Moser et al, 2011—U.S. Pat. No. 7,985,265), including the use of microprocessor-control to adjust damping properties. The inherent problem with damping control of the ankle is the associated loss of energy that occurs. One system exists that uses a motor to change the equilibrium point of a spring-like prosthetic foot (Jonsson et al, 2011—U.S. Pat. No. 8,048,172). However, this system requires multiple steps on a new terrain before it is able to adapt to the new slope. A more desirable system would adapt to different sloped surfaces on each and every step of walking. Lastly, powered ankle-foot systems are being developed (Hugh Herr, Massachusetts Institute of Technology; Thomas Sugar, Arizona State University; Michael Goldfarb, Vanderbilt University). These systems all actively push the prosthesis user with a motor during various times in the gait cycle and require large power sources, e.g., heavy batteries and motors. The only currently available system on the market (iWalk BiOM) is expensive, making it impractical for the majority of lower limb prosthesis users. Also, the high power requirements necessitate carrying additional batteries and frequent charging of batteries.

SUMMARY OF THE INVENTION

The invention concerns an ankle-foot prosthesis. In one example embodiment the ankle-foot prosthesis comprises a foot plate, an ankle frame, a yoke, a hydraulic damper, a stiffness member, and a fluid circuit. The foot plate includes a rear portion and a forward deflectable portion. The ankle frame includes anterior and posterior portions and an apex portion. The posterior portion of the ankle frame attaches to the rear portion of the foot plate. The anterior portion of the ankle frame includes a curved surface inclined upwardly relative to the foot plate and forwardly toward the forward deflectable portion of the foot plate. The curved surface forms a roll-over surface for limiting a dorsiflexion deflection of the forward deflectable portion of the foot plate by a direct engagement therewith. The yoke includes front and rear end portions, and a fulcrum point therebetween. The yoke is pivotally connected to the apex portion of the ankle frame at the fulcrum point thereof and includes a member for attaching to a prosthetic leg. The hydraulic damper has a first end pivotally connected to the rear end portion of the yoke and a second end pivotally connected to the ankle frame. The stiffness member is disposed in parallel to the damper. The fluid circuit is for controlling extension and compression of the damper.

By way of example, the fluid control circuit includes a cutoff valve for allowing dorsiflexion and plantarflexion of the ankle-foot prosthesis. In another example, the cutoff valve allows movement of the ankle-foot prosthesis during a gait cycle between prosthetic side toe off and the next prosthetic side foot flat. Further by way of example, the cutoff valve allows extension of the damper during a gait cycle at least between prosthetic side toe off and 0 to 0.13 seconds thereafter. In a particular example, the fluid control circuit further comprises first and second check valves. The first check valve is arranged in parallel with the second check valve. The first check valve is for allowing compression of the damper and the second check valve for allowing extension of the damper. In a particular example, the fluid control circuit further comprises at least one variable fluid-flow resistor and first and second check valves. The at least one variable fluid-flow resistor is for adjusting hydraulic fluid resistance in plantarflexion. The first check valve is arranged in parallel with the second check valve. The first check valve is for allowing compression of the damper and the second check valve for allowing extension of the damper. In a particular example, the fluid control circuit further comprises first and second check valves and first and second variable fluid-flow resistors. The first check valve is arranged in parallel with the second check valve. The first check valve is for allowing compression of the damper and the second check valve is for allowing extension of the damper. The first variable fluid-flow resistor is arranged in parallel with the second variable fluid-flow resistor. The first variable fluid-flow resistor is for adjusting hydraulic fluid resistance in plantarflexion and the second variable fluid-flow resistor for adjusting hydraulic fluid resistance in dorsiflexion.

In an example, the ankle-foot prosthesis further comprises at least one check valve for the fluid control circuit for allowing compression of the damper. In a particular example, the fluid circuit further comprises a cutoff valve for allowing dorsiflexion of the ankle-foot prosthesis.

In a further example, the ankle-foot prosthesis further comprise at least one variable fluid-flow resistor for the fluid control circuit for adjusting hydraulic fluid resistance in dorsiflexion, plantarflexion, or both. In a particular example, the fluid control circuit further comprises first and second check valves and first and a cutoff valve. The first check valve is arranged in parallel with the second check valve. The first check valve is for allowing compression of the damper and the second check valve is for allowing extension of the damper. The cutoff value is for allowing dorsiflexion of the ankle-foot prosthesis.

By way of example, the stiffness member comprises a spring or an elastic member. In a further example the spring comprises at least one of a compression spring, an extension spring, a compression tube spring, an extension tube spring, and a curved leaf spring.

By way of example, the fluid control circuit further comprises first and second check valves. The first check valve is arranged in parallel with the second check valve. The first check valve allows compression of the damper and the second check valve allows extension of the damper. In a particular example, the fluid control circuit further comprises first and second cutoff valves. The first cutoff valve is arranged in parallel with the second cutoff valve. The first cutoff valve is for allowing plantarflexion of the ankle-foot prosthesis and the second cutoff valve is for allowing dorsiflexion of the ankle-foot prosthesis. In a particular example, the fluid control circuit further comprises first and second variable fluid-flow resistors and a cutoff valve. The first variable fluid-flow resistor arranged in parallel with the second variable fluid-flow resistor. The first variable fluid-flow resistor is for adjusting hydraulic fluid resistance in plantarflexion and the second variable fluid-flow resistor is for adjusting hydraulic fluid resistance in dorsiflexion. The cutoff valve is for allowing dorsiflexion of the ankle-foot prosthesis. In a particular example, the fluid control circuit further comprises first and second cutoff valves and first and second variable fluid-flow resistors. The first cutoff valve is arranged in parallel with the second cutoff valve. The first cutoff valve is for allowing plantarflexion of the ankle-foot prosthesis and the second cutoff valve is for allowing dorsiflexion of the ankle-foot prosthesis. The first variable fluid-flow resistor is arranged in parallel with the second variable fluid-flow resistor. The first variable fluid-flow resistor is for adjusting hydraulic fluid resistance in plantarflexion, the second variable fluid-flow resistor is for adjusting hydraulic fluid resistance in dorsiflexion.

In an example, the fluid control circuit further comprises first and second cutoff valves. The first cutoff valve is arranged in parallel with the second cutoff valve. The first cutoff valve allows plantarflexion of the ankle-foot prosthesis and the second cutoff valve allows dorsiflexion of the ankle-foot prosthesis.

By way of example, the fluid control circuit further comprises first and second variable fluid-flow resistors. The first variable fluid-flow resistor is arranged in parallel with the second variable fluid-flow resistor. The first variable fluid-flow resistor is for adjusting hydraulic fluid resistance in plantarflexion and the second variable fluid-flow resistor is for adjusting hydraulic fluid resistance in dorsiflexion.

In an example, the fluid control circuit further comprises at least one variable fluid-flow resistor for adjusting fluid resistance in plantarflexion. In a particular example, the fluid control circuit further comprises first and second check valves and first and second cutoff valves. The first check valve is arranged in parallel with the second check valve. The first check valve is for allowing compression of the damper and the second check valve is for allowing extension of the damper. The first cutoff valve is arranged in parallel with the second cutoff valve. The first cutoff valve is for allowing plantarflexion of the ankle-foot prosthesis and the second cutoff valve is for allowing dorsiflexion of the ankle-foot prosthesis.

ASPECTS OF THE INVENTION

The present disclosure is directed to various aspects of the present invention.

One aspect of the present invention is to provide an ankle-foot prosthesis that allows a user to have a more natural, and thus more comfortable gait.

Another aspect of the present invention is to provide an ankle-foot prosthesis that is more energy-efficient when used for walking or other gait.

Another aspect of the present invention is to provide an ankle-foot prosthesis that is simple in design and construction and, thus, uses fewer parts or components, and requires no or low maintenance.

Another aspect of the present invention is to provide an ankle-foot prosthesis that is compact and more durable than, for example, those using multitude of mechanical parts leading to a higher rate of failure.

Another aspect of the present invention is provide an ankle-foot prosthesis that resists or prevents undesirable backward swing, which could lead to imbalance or injury.

Another aspect of the present invention is to provide an ankle-foot prosthesis that is quieter, light-weight, and less clumsy to use, and thus more user-friendly.

Another aspect of the present invention is to provide an ankle-foot prosthesis that automatically adapts to different sloped walking surfaces on every step of walking.

Another aspect of the present invention is to provide an ankle-foot prosthesis that can easily switch into a stable mode for standing or swaying, for example, when washing the dishes.

Another aspect of the present invention is to provide an ankle-foot prosthesis, which includes a foot plate, an ankle frame attached to the foot plate, a yoke pivotally connected to the ankle frame and including a member for attaching to a leg, a damper having a first end connected to the yoke and a second end connected to the ankle frame, and a control mechanism for switching the damper between low and high settings.

Another aspect of the present invention is to provide an ankle-foot prosthesis, which includes a foot plate, an ankle frame attached to the foot plate and including anterior and posterior portions and an apex portion, a yoke pivotally connected to the apex portion of the ankle frame and including a member for attaching to a leg, a hydraulic damper having a first end pivotally connected to the yoke and a second end connected to the posterior portion of the ankle frame; a spring disposed in parallel to the damper, and a control mechanism for controlling extension and compression of the damper.

Another aspect of the present invention is to provide a method of using an ankle-foot prosthesis by an amputee, which includes a) providing an ankle-foot prosthesis including i) a foot plate, ii) an ankle frame attached to the foot plate, iii) a yoke pivotally connected to the ankle frame and including a member for attaching to a leg, iv) a damper having a first end connected to the yoke and a second end connected to the ankle frame, and v) a control mechanism for switching the damper between low and high settings to selectively control extension, compression, or both extension and compression thereof; b) attaching the ankle-foot prosthesis to a lower limb of the amputee; c) allowing the amputee to ambulate for at least one gait cycle, wherein the gait cycle includes i) the ankle-foot prosthesis in an initial neutral position to a first plantarflexion position such that the foot plate is substantially flat on a walking surface, and ii) the ankle-foot prosthesis in a toe-off plantarflexion position; d) switching the damper to the high extension setting substantially at the first plantarflexion position; and e) switching the damper to the low extension setting substantially at the toe-off plantarflexion position.

In summary, the present invention is directed to a prosthetic ankle-foot device that can automatically adapt its function for walking on different sloped surfaces, allowing its user to walk on these surfaces with more stability and confidence. The invention also provides a stable mode for standing and swaying tasks (e.g., washing the dishes).

BRIEF DESCRIPTION OF THE DRAWINGS

One of the above and other aspects, novel features and advantages of the present invention will become apparent from the following detailed description of the non-limiting preferred embodiment(s) of invention, illustrated in the accompanying drawings, wherein:

FIG. 1 is a perspective view of a preferred embodiment of the ankle-foot prosthesis in accordance with the present invention;

FIG. 2 illustrates a blank timing plot for the ankle-foot prosthesis of the present invention, which can be used to create any gait cycle that begins with prosthetic heel contact (HC) and continues until the next HC (100% of the gait cycle);

FIG. 3 illustrates a plot of the theoretical vertical load on the prosthesis;

FIG. 4 illustrates a plot of the load on spring/damper combination at the start of stance phase, the heel of the prosthesis making contact with the surface, placing a compressive load on the spring/damper combination;

FIG. 5 illustrates a plot of the damping values in each direction for the damper during the gait cycle;

FIG. 6 illustrates a plot of the cylinder (damper) length;

FIG. 7 shows three hydraulic circuit symbols used for fluid circuit schematics shown in FIGS. 8-16;

FIGS. 8-16 disclose various preferred embodiments of the fluid control circuit (FCC) used in the present invention;

FIG. 17 discloses various types of stiffness or elastic members for use in the present invention;

FIG. 18 is a perspective view of a second embodiment of the ankle-foot prosthesis in accordance with the present invention;

FIG. 19 discloses the ankle-foot prosthesis of FIG. 18, showing the ankle in a plantarflexed state;

FIG. 20 is a view similar to FIG. 19, showing the ankle in a neutral state, after dorsiflexion from the ankle angle in FIG. 19, and extension of the stiffness member compared with its position in FIG. 19;

FIG. 21 shows the ankle-foot prosthesis of FIG. 18, showing the ankle in a neutral state;

FIG. 22 is a view similar to FIG. 21, showing plantarflexion of the ankle and compression of the stiffness member when compared with its position in FIG. 21;

FIG. 23 is a rear perspective view of a third embodiment of the ankle-foot prosthesis in accordance with the present invention;

FIG. 24 is a cross-sectional view taken along line 24-24 of FIG. 23, showing foot flat adapted to a declined surface (ankle plantarflexed relative to foot flat on a level surface);

FIG. 25 is a view similar to FIG. 24, showing foot flat adapted to a level surface (ankle plantarflexed relative to a swing phase ankle angle);

FIG. 26 is a view similar to FIG. 24, showing foot flat adapted to an inclined surface (ankle dorsiflexed relative to foot flat on a level surface);

FIG. 27 is a side cross-sectional view of a fourth embodiment of the ankle-foot prosthesis in accordance with the present invention;

FIG. 28 is a side view of a fifth embodiment of the ankle-foot prosthesis in accordance with the present invention;

FIG. 29 is a side cross-sectional view of a sixth embodiment of the ankle-foot prosthesis in accordance with the present invention;

FIG. 30 is side cross-sectional view of a seventh embodiment of the ankle-foot prosthesis in accordance with the present invention;

FIG. 31 is a side cross-sectional view of an eighth embodiment of the ankle-foot prosthesis in accordance with the present invention;

FIG. 32 is side cross-sectional view of a ninth embodiment of the ankle-foot prosthesis in accordance with the present invention;

FIG. 33 is a side cross-sectional view of the tenth embodiment of the ankle-foot prosthesis in accordance with the present invention;

FIG. 34 is a side cross-sectional view of an eleventh embodiment of the ankle-foot prosthesis in accordance with the present invention; and

FIGS. 35-45 disclose various alternate preferred embodiments of the fluid control circuit (FCC) used in the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) OF THE INVENTION

Referring to FIG. 1, a preferred embodiment of the ankle-foot prosthesis AFP will be described. As shown, a generally pyramid-like attachment part 10, consistent with standard endoskeletal componentry in prosthetics, is provided at the top of a yoke 12, on the opposite ends of which are holes drilled for front and rear pivotal attachments 14 and 16, respectively. The rear pivot 16 attaches to one end 17 of a preferably microprocessor controlled damper device 18 (to be described in more detail below). A neutralizing spring 20 is connected in parallel to the damper 18, such that its length change is equal to that of the damper.

The damper device 18 attaches on its other end 19 to an ankle frame 22, which has a yoke opening 24 and holes drilled at its posterior end 26 to pivotally attach to the damper 18 using a shaft 28. The “ankle” of the device AFP is a shaft 30 connecting the yoke 12 with the apex 29 of the ankle frame 22.

The ankle frame 22 attaches with one or more bolts (or other suitable fixation means) to the rear portion 32 of a flexible, yet deflectable rigid foot plate 34. The anterior end 36 of the ankle frame 22 includes a follower or upwardly inclined surface 38 that limits the deflection of the foot plate 34, such that the ankle-foot device AFP will take a biomimetic ankle-foot roll-over shape during walking. The geometry of the surface 38 is such that it provides the correct roll-over shape when the “ankle” is locked into a plantarflexed angle at the time of foot flat of walking, i.e., an angle of about 10 to 15 degrees.

The damper 18 is designed to have different values for compression and extension damping that can be controlled by using a suitable microprocessor (not shown). Specifically, the microprocessor would have the capability to variably manage the timing for opening and closing the valves and the variable restriction element, shown in FIG. 7 and described below in more detail. For walking, the compression damping is set to a very low level and is unchanged throughout the gait cycle. The extension damping for walking is set to a very high level at the beginning of the gait cycle and changes to a very low level damping at the time of toe-off (which must be sensed using one or more sensors of force, acceleration, or other properties). The extension damping can remain at a low level of damping for at least the time needed to return the ankle to a neutral or dorsiflexed position for swing phase and at most the time to the next foot flat event of the prosthesis. For standing, both compression and extension damping levels can be controlled to be very high, providing a flatter effective shape and increasing the stability of the prosthesis user.

For a normal gait cycle, the heel of the system, shown in FIG. 1, will contact the surface and the foot will “find the surface” under a low stiffness of the neutralizing spring 20. The compression damping is low so the ankle reacts primarily in this phase of gait to the neutralizing spring 20. The compression damping could be altered for different patients, but would be static throughout the gait cycle once set by the prosthetist or the user. After foot flat, the ankle is at a maximally plantarflexed position and would normally start to dorsiflex. In this invention, the extension damping would be very high, essentially locking the ankle in a plantarflexed position. As the person rolls over the device, the flexible footplate 34 flexes up to the follower 38, producing a biomimetic ankle-foot roll-over shape. After the opposite foot contacts the ground, energy is returned from the flexible footplate 34 and the ankle goes into late stance plantarflexion (the angle at which it was set to at foot flat). As the prosthetic device leaves the walking surface (toe-off), the extension damping switches a very low level, allowing the neutralizing spring 20 to bring the ankle back to a neutral or slightly dorsiflexed position, which allows for toe clearance during the swing phase. The damping level needs to be low enough to allow the ankle to return to neutral during the first third or half of the swing phase. After the ankle has returned to neutral or a slightly dorsiflexed position and before the prosthesis gets to foot flat on the next cycle, the extension damping should shift to a very high level for the next cycle.

The operation of the ankle in the manner described above, allows the foot to “find the surface” during walking. For uphill walking, the foot finds the surface in a more dorsiflexed position compared with that for level walking and thus the equilibrium point of the ankle is set in more dorsiflexion. For downhill walking, the foot finds the surface in a more plantarflexed position compared with that for level walking. In this way, the ankle-foot device automatically adapts to different terrain on each and every step of walking. Also, the control mechanism for the ankle would be relatively simple in that it only changes the extension damping of the damper 18 between two levels during walking. The control mechanism also needs to determine when the ankle-foot system is in “walking” and “standing” modes and switch its behavior. For “standing” mode, the damping for both compression and extension of the damper 18 should be set to very high, as mentioned earlier.

Referring to FIGS. 2-6, various timing plots for the ankle-foot prosthesis AFP of the invention will now be described. The blank plot of FIG. 2 can be used to create any gait cycle that begins with prosthetic heel contact (HC) and continues until the next HC (100% of the gait cycle). For the first 10% of the gait cycle, both feet are on the ground as weight transitions from the opposite limb to the prosthetic limb. At approximately 10%, the opposite toe is lifted from the floor (opposite toe-off or OTO). When the opposite toe is off the ground, only the prosthetic foot is in contact with the walking surface and supporting the weight of the body, so this is considered prosthetic single-limb-support (40% of the gait cycle). This also corresponds to the period of highest load on the prosthetic limb as the user rolls over their foot. At approximately 50% of the gait cycle, the opposite heel contacts the surface (OHC) and weight begins to transition from the prosthetic limb to the sound limb. At approximately 60% of the gait cycle, the prosthetic limb is lifted off the surface (toe-off or TO) and the remainder of the gait cycle is sound side single limb support as the prosthetic limb swings through. (These numbers are approximate.) Modern conventional usages are changing to use Initial Contact, instead of Heel Contact, because the heel is not always the first part of the foot to come into contact with the walking surface (such as persons with drop-foot syndrome or equinus deformity), but for this invention the two should be equivalent.

FIG. 3 illustrates a plot of the theoretical vertical load on the prosthesis. The plot shows the standard double-hump shape of the vertical component of the ground reaction force vector from standard gait analyses. The first peak corresponds to load acceptance on the prosthetic side, where the prosthesis is used to brake the descent of the body center of mass. The second peak occurs as the user pushes off of their prosthetic side and begins to transition onto their sound side (and occurs around opposite heel contact (OHC). The vertical load drops to 0 as the toe leaves the surface (toe-off, TO) and remains there through swing phase. During single limb support, the vertical load can reach levels that are greater than body weight. For slow walking, the peak load could be 1.1×BW (Body Weight), whereas for fast walking or sudden stumbles the peak load could be upwards of 1.5×BW (Body Weight).

FIG. 4 illustrates a plot of the load on the spring/damper combination at the start of stance phase, the heel of the prosthesis making contact with the surface, placing a compressive load on the spring/damper combination. This load continues until the foot is resting flat against the walking surface. At that time, the user begins to roll over their prosthetic foot. The damper is set to a high extension damping level, so it does not extend, thus the spring becomes an internal stress and when the user starts to roll over their foot, the compressive load very rapidly switches to a small tensile load and then the tensile load gradually increases as the user rolls over the foot. Near the end of stance phase, the user has rolled over the prosthesis and begins to lift the foot from the ground, reducing the tensile force on the spring-damper combination, until the toe is lifted from the surface. At this point the spring is still applying an internal force within the system but is unable to actuate motion because the damper is still in a high extension damping state and resists the spring. When the load is removed, the hydraulic cutoff valve (fluid equivalent of a switch) is opened allowing the spring to extend and quickly return the foot to a neutral ankle position for swing phase.

FIG. 5 illustrates a plot of the damping values in each direction for the damper during the gait cycle. In the direction of compression, the damping during walking should be low enough to allow the foot to quickly reach the surface, but not so low that the foot makes a slapping sound when it encounters the surface. The precise value will be dependent on the weight, foot length, and gait mechanics of each individual user and will parallel standard clinical practice for adjusting similar properties of other commercially available components. Ideally the precise amount of damping will be adjustable by the prosthetist for customization to the individual. For long-term standing tasks (doing the dishes, standing at a work station at work, etc.), an ideal embodiment would also be able to raise the compression damping to near infinite (through the use of a cutoff valve) to improve stability when loading the heel, however this function is not of use during walking tasks. The extension damping must be high or nearly infinite (closed cutoff valve, effectively fixing the length of the damper against extension) when the user begins to roll over the foot (in the plot, this is shown as approximately 5% of the gait cycle) and must remain so until the point of toe-off. At the very beginning of swing phase, the cutoff valve is opened, allowing the damper to extend under the load from the spring until the prosthesis has returned to a neutral position (ideally within 0.13 seconds). After the foot has returned to a neutral position for swing phase, the cutoff valve can be closed again. Thus, the cutoff valve could close as early as 0.13 seconds after toe-off or as late as at the moment of foot flat (approximated as 5% of the next gait cycle, but varies by step and surface conditions).

FIG. 6 illustrates a plot of the cylinder (damper) length. The current model of the novel ankle-foot prosthesis has a damper with a fully extended length of 70 mm, and a fully compressed length of 50 mm. This corresponds to a 30-35 degree range of ankle motion. Other designs may use different numbers, however the relationships will still hold. When walking on level ground, the ankle will plantarflex, allowing the foot plate to become flat on the walking surface, during the first approximately 5-10% of the gait cycle. Once the foot is flat on the surface and the user begins to roll over the foot, the damper is unable to extend, so the spring-damper combination remains at its partially extended length throughout the remainder of stance phase. When the prosthesis is lifted from the ground (TO), the cutoff valve is opened and the spring returns the foot to a neutral position for swing phase. When walking uphill, the foot will be flat on the surface in a more dorsiflexed position, so the foot will not plantarflex much during early stance, whereas when walking downhill the foot will plantarflex much more before it is flat on the surface.

FIG. 7 shows three hydraulic circuit symbols used for fluid circuit schematics shown in FIGS. 8-16. The symbol used for the check valve 40 is most commonly used to refer to a ball valve, although other types of check valves may also be used. The variable restriction 42 is the damping element of the circuit. There is some damping (fluid resistance) due to friction in the lines and passing through other elements of the circuit, so there is a minimum level of damping regardless. Thus, in some embodiments, the restriction element is not present indicating the use of innate damping alone. The reference numeral 44 designates a cutoff value.

FIG. 8 discloses the most complex and powerful embodiment of the fluid control circuit (FCC). The fluid circuit splits into two branches. Each branch has a check valve 40 oriented to permit fluid flow in either compression or extension alone, thereby separating the extension and compression properties for the damper. In the compression line, there is provided a variable restriction element 42, where the prosthetist could adjust the damping level to optimize the prosthesis for the individual patient. In the extension line, there is also a variable restriction element 42 that could be adjusted to tune the neutralization damping after toe-off to address any issues with the speed of neutralization or with noises that could arise from underdamped neutralization. Both lines have independent cutoff valves 44, allowing the extension damping to be raised to nearly infinite as appropriate during each step and then both cutoff valves to be closed for standing tasks, making a stable base of support for the user.

FIG. 9 discloses an embodiment that contains all of the adjustability of the embodiment of FIG. 8, but only a single cutoff valve 44 is used on a common line to arrest both compression and extension of the damper simultaneously. The advantage of this system over FIG. 8 is fewer parts (one fewer cutoff valve). The disadvantage of this system compared with the embodiment of FIG. 8 is that sensors would need to be in place to insure that the cutoff valve would open at the time of toe-off and close at exactly the time of foot flat to prevent unexpected instability and potential falls.

FIG. 10 discloses an embodiment that is similar to the embodiment of FIG. 8, except it does not have a variable restriction element 42 on the extension line. Therefore, there is no way to tune the extension damping for neutralization after toe-off. This embodiment is more efficient because of the reduced number of components (saving weight, size and cost) but only if the fluid circuit can be optimized to allow the foot to return to neutral within 0.13 seconds without oscillating or making loud noises when it reaches the neutral position. This system retains the ability to cutoff both compression and extension for standing tasks.

FIG. 11 discloses an embodiment similar to the embodiments presented in both FIGS. 9-10, however, it lacks the ability to adjust extension damping and has a single cutoff valve 44 to arrest motion in both extension and compression simultaneously. This is even more efficient, having removed two components from the system and saving weight, size, and cost. The challenges with this embodiment have been discussed in paragraphs [0039] and [0040].

The embodiment of FIG. 12 is similar to the embodiment of FIG. 8, except that it does not have a cutoff valve 44 in the compression line. For this reason, the compression damping will remain constant throughout the gait cycle and compression motion will not be arrested during standing tasks. Both lines have adjustable damping from the variable restriction elements and the extension line still has a cutoff valve. This embodiment could be realized in a purely passive system, where the biomechanics of walking (e.g. load on the prosthesis) control the opening and closing of the cutoff valve. For example, a spring-loaded hinge or telescoping element within the prosthesis could close the cutoff valve when load is applied to the prosthesis and open the cutoff valve when load is removed from the prosthesis. It would not be practical to rely on this type of physical input to control the compression line for standing tasks, so none of the previous embodiments would be practical for purely passive operation.

The embodiment of FIG. 13 is similar to the embodiments of FIGS. 10 and 12, however, it also lacks the ability to adjust the damping in the extension line but saves weight, size, and cost. But it lacks the ability to cutoff the compression line and therefore does not have the standing stability feature of the earlier embodiments.

The embodiment of FIG. 14 is similar to the embodiment of FIG. 8, but lacks variable dampers 42. The level of resistance for compression can be adjusted by the prosthetist by changing springs or by pre-compressing the spring. Otherwise the function would be the same.

The embodiment of FIG. 15 is similar to the embodiment of FIG. 9, but lacks variable dampers 42. The level of resistance for compression can be adjusted by the prosthetist by changing springs or by pre-compressing the spring.

FIG. 16 shows our simplest embodiment. There is a check valve 40 to permit compression, but not extension, and then when the foot is to be neutralized the cutoff valve is opened, permitting extension by bypassing the check valve 40. Ideally the cutoff valve 44 would be mechanically opened and closed by loads applied during the gait cycle, resulting in a purely passive system with no batteries, microprocessors, or other electronic components, though this could be actuated by a solenoid or other actuator and controlled by electronics.

FIGS. 17-45 are directed to various alternate embodiments of the stiffness/elastic members, the ankle-foot prosthesis, and the fluid control circuits used in the present invention. By way of a summary: FIG. 17 discloses illustrative examples of stiffness/elastic members; FIG. 18-22 show a second embodiment of the ankle-foot prosthesis AFP2 that is similar to the embodiment shown in FIG. 1; FIGS. 23-26 show a third embodiment of the ankle-foot prosthesis AFP3, in which the damper device is connected to the front end portion of the yoke; FIG. 27 discloses a fourth embodiment of the ankle-foot prosthesis AFP4, in which the damper and the spring are positioned in the front of the yoke; FIGS. 28-33 disclose fifth to tenth embodiments of the ankle-foot prosthesis AFP5-AFP10, respectively, wherein the stiffness member is separate from the damper device; FIG. 34 discloses the eleventh embodiment of the ankle-foot prosthesis AFP11, in which the damper device is connected to a rear portion of the yoke; and FIGS. 35-45 disclose alternate embodiments of the fluid control circuits. (It is noted herewith that for clarity, similar components have been designated by the same reference numerals in the embodiments shown in FIGS. 18-34. Further, similar components of the FCCs shown in FIGS. 8-16, have been designated by the same reference numerals in FIGS. 35-45.)

Referring to FIG. 17, various types of stiffness members can be used. Representative non-limiting examples include a compression spring 50, an extension spring 52, a compression tube spring 54, an extension tube spring 56, a curved leaf spring 58, and an elastic bumper 60.

Referring to FIGS. 18-22, a second embodiment of the ankle-foot prosthesis AFP2 will now be described. As shown, an attachment part 62, consistent with endoskeletal componentry in prosthetics, is provided at the top of a yoke 64 for attaching to a prosthetic leg PL (see FIG. 19, for example). The yoke 64 includes front and rear end portions 66 and 68, respectively, and a fulcrum point 70 therebetween. The rear end portion 68 is pivotally attached to an upper end 72 of a preferably microprocessor-controlled damper device 74, via a shaft 75. The damper device 74 is similar to and functions in the same manner as the damper 18, described above. Preferably, a compression spring 50 is connected in parallel to the damper 74, such that its length change is equal to that of the damper. As shown, the compression spring 50 extends during dorsiflexion (FIG. 20), and compresses during plantarflexion (FIG. 22).

The damper device 74 attaches on its lower end 76 to an ankle frame 78, which has a yoke opening 80 and holes drilled at its posterior end 82 to pivotally attach to the damper device 74 via a shaft 84. As noted above with respect to the embodiment disclosed in FIG. 1, the “ankle” of the device AFP2 is a shaft 86 that connects the fulcrum point 70 of the yoke 64 with the apex 88 of the ankle frame 78.

The ankle frame 78 attaches with one or more bolts (or other suitable fixation means) to the rear portion 90 of a flexible foot plate 92. The anterior end 94 of the ankle frame 78 includes a follower or upwardly inclined surface 96 that limits the deflection of the foot plate 92, such that the ankle-foot device AFP2 will take a biomimetic ankle-foot roll-over shape during walking. The geometry of the surface 96 is similar to and functions in the same manner as the surface 38 described above with respect to the embodiment shown in FIG. 1.

As best shown in FIGS. 19-22, the front end 66 of the yoke 64 remains free, while the rear end thereof 68 is connected to the damper 74. As shown in FIGS. 19-20, the damper 74 extends during dorsiflexion, and compresses during plantarflexion, as shown in FIGS. 21-22.

The third embodiment of the ankle-foot prosthesis AFP3, shown in FIGS. 23-26, is similar to the second embodiment shown in FIGS. 18-22, except that the upper end 72 of the damper 74 is pivotally connected to the front end portion 66 of the yoke 64, leaving the rear end portion 68 thereof free. In addition, as best shown in FIG. 23, the damper 74, along with the extension spring 52 extends through the yoke opening 80, from the posterior end portion 82 of the ankle frame 78, towards the front thereof. As shown in FIG. 24 (with cosmetic cover CC), the foot flat is adapted to a declined surface DS (the ankle plantarflexed relative to foot flat on a level surface), with the spring 52 more extended. Likewise, as shown in FIG. 25 (with cosmetic cover CC), the foot flat is adapted to a level surface LS (the ankle plantarflexed relative to a swing phase of ankle angle), with normal extension of spring 52. In the same manner, as shown in FIG. 26 (with cosmetic cover CC), the foot flat is adapted to an inclined surface IS (the ankle dorsiflexed relative to foot flat on a level surface), with less extension of the spring 52. This configuration provides a long rest length for the damper.

FIG. 27 discloses a fourth embodiment of the ankle-foot prosthesis AFP4, wherein the damper device 74 and the spring 52 are both positioned in the anterior end portion 94 of the ankle frame 78, and the upper end 72 of the damper is pivotally connected to the front end portion 66 of the yoke 64. This configuration offers a short action of the damper and the stiffness member.

As noted above, FIGS. 28-33 disclose fifth through tenth embodiments of the ankle-foot prosthesis AFP5 to AFP10, wherein the stiffness member (for example, spring 52) is positioned separate from the damper device 74. In particular, FIG. 28 discloses the fifth embodiment AFP5, wherein the spring 52 is wedged between the front end portion 66 of the yoke 64, and the anterior end portion 94 of the ankle frame 74. This configuration allows varying sizes/lengths for the stiffness member and adjustability thereof independent of the damper, thus offering easier customization to a specific user.

FIG. 29 discloses the sixth embodiment of ankle-foot prosthesis AFP6, wherein the extension tube spring 56 functions as the stiffness member that is secured in place by a pin 98 in a recess 100 of the ankle frame 78. It is noted that the extension tube spring 56 may be substituted by other types of stiffness members, such as elastic tensile, cord/loop, similar to a bundle of rubber bands.

FIG. 30 discloses the seventh embodiment of the ankle-foot prosthesis AFP7, which is similar to the fifth embodiment of FIG. 28, except that the spring 50 is positioned between the rear end portion 68 of the yoke 64, and an abutment 102 of the ankle frame 78. In addition, the positioning of the damper 74 is similar to that shown in the third embodiment AFP3 of FIG. 23.

FIGS. 31-33 disclose eighth, ninth and tenth embodiments of the ankle-foot prosthesis AFP8, AFP9, AFP10, which are similar to the embodiments shown in FIG. 30, except that the spring 50 is substituted by a curved leaf spring 58, a compression tube spring 54, and an elastic bumper 60, respectively. Additionally, the damper device 74 is positioned in the same manner as in the third embodiment shown in FIG. 23, offering the advantage(s) of a long rest length for the damper.

The eleventh embodiment of the ankle-foot prosthesis AFP11, shown in FIG. 34, is somewhat similar to the fourth embodiment of FIG. 27, except that the upper end 72 of the damper 74 is pivotally connected to the rear end portion 68 of the yoke 64, and the lower end 76 of the damper 74 is pivotally connected to the ankle frame 78, adjacent the anterior end portion 94 thereof. This configuration offers the advantage(s) of providing a more compact arrangement of components that will more easily fit within a cosmetic cover and shoe.

Referring now to FIGS. 35-45, showing fluid control circuits (FCC). FIG. 35 illustrates a simple embodiment, but that requires precise control to achieve the intended function of the ankle. FIG. 35 is a simpler version of FIG. 15. It works identically to the FCC in FIG. 15, but does not require the two check valves 40 shown in FIG. 15. The cutoff valve 44 must be open from toe-off until foot flat of the prosthesis, then it must be closed from foot flat until toe-off. The FCC depictions in FIGS. 8-16 and 35 pertain to embodiments where the damper connects to the rear portion of the yoke 68 (as in FIGS. 1, 18-22, 28, 29, and 34), whereas the FCC depictions in FIGS. 36-45 pertain to embodiments where the damper connects to the front portion of the yoke 66 (as in FIGS. 23-27 and 30-33).

FIG. 36 discloses the most complex and powerful embodiment of the fluid control circuit (FCC). The fluid circuit splits into two branches. Each branch has a check valve 40 oriented to permit fluid flow in either compression or extension alone, thereby separating the extension and compression properties for the damper. In the extension line, there is provided a variable restriction element 42, where the prosthetist could adjust the damping level to optimize the prosthesis for the individual patient. In the compression line, there is also a variable restriction element 42 that could be adjusted to tune the neutralization damping after toe-off to address any issues with the speed of neutralization or with noises that could arise from underdamped neutralization. Both lines have independent cutoff valves 44, allowing the compression damping to be raised to nearly infinite as appropriate during each step (by selectively closing the compression line cutoff valve) and then both cutoff valves to be closed for standing tasks, making a stable base of support for the user.

FIG. 37 discloses an embodiment that contains all of the adjustability of the embodiment of FIG. 36, but only a single cutoff valve 44 is used on a common line to arrest both compression and extension of the damper simultaneously. The advantage of this system over FIG. 36 is fewer parts (one fewer cutoff valve). The disadvantage of this system compared with the embodiment of FIG. 36, is that sensors would need to be in place to ensure that the cutoff valve 44 would open at the time of toe-off and close at exactly the time of foot flat to prevent unexpected instability and potential falls.

FIG. 38 discloses an embodiment that is similar to the embodiment of FIG. 36, except it does not have a variable restriction element 42 on the compression line. Therefore, there is no way to tune the compression damping for neutralization after toe-off. This embodiment is more efficient because of the reduced number of components (saving weight, size and cost) but only if the fluid circuit can be optimized to allow the foot to return to neutral within 0.13 seconds without oscillating or making loud noises when it reaches the neutral position. This system retains the ability to cutoff both compression and extension for standing tasks.

FIG. 39 discloses an embodiment similar to the embodiments presented in both FIGS. 37-38, however, it lacks the ability to adjust compression damping and has a single cutoff valve 44 to arrest motion in both extension and compression simultaneously. This is even more efficient, having removed two components from the system and saving weight, size, and cost. The challenges with this embodiment have been discussed above in paragraphs [0081] and [0082].

The embodiment of FIG. 40 is similar to the embodiment of FIG. 36, except that it does not have a cutoff valve 44 in the extension line. For this reason, the extension damping will remain constant throughout the gait cycle and extension motion will not be arrested during standing tasks. Both lines have adjustable damping from the variable restriction elements and the compression line still has a cutoff valve 44. This embodiment could be realized in a purely passive system, where the biomechanics of walking (e.g. load on the prosthesis) control the opening and closing of the cutoff valve 44. For example, a spring-loaded hinge or telescoping element within the prosthesis could close the cutoff valve 44 when load is applied to the prosthesis and open the cutoff valve 44 when load is removed from the prosthesis. It would not be practical to rely on this type of physical input to control the extension line for standing tasks, so none of the previous embodiments would be practical for purely passive operation.

The embodiment of FIG. 41 is similar to the embodiments of FIGS. 38 and 40, however, it also lacks the ability to adjust the damping in the compression line but saves weight, size, and cost. But it lacks the ability to cutoff the extension line and therefore does not have the standing stability feature of the earlier embodiments.

The embodiment of FIG. 42 is similar to the embodiment of FIG. 36, but lacks variable dampers 42. The level of resistance for extension can be adjusted by the prosthetist by changing springs or by pre-compressing the spring. Otherwise the function would be the same.

The embodiment of FIG. 43 is similar to the embodiment of FIG. 37, but lacks variable dampers 42. The level of resistance for extension can be adjusted by the prosthetist by changing springs or by pre-compressing the spring.

FIG. 44 shows a simple embodiment. There is a check valve 40 to permit extension, but not compression, and then when the foot is to be neutralized the cutoff valve is opened, permitting compression by bypassing the check valve 40. Ideally, the cutoff valve 44 would be mechanically opened and closed by loads applied during the gait cycle, resulting in a purely passive system with no batteries, microprocessors, or other electronic components, though this could be actuated by a solenoid or other actuator and controlled by electronics.

FIG. 45 shows our simplest embodiment, but that requires precise control to achieve the intended function of the ankle, and is a simpler version of FIG. 43. It works identically to the FCC in FIG. 43, but does not require the two check valves 40 shown in FIG. 43.

While this invention has been described as having preferred sequences, ranges, steps, order of steps, materials, structures, symbols, indicia, graphics, color scheme(s), shapes, configurations, features, components, or designs, it is understood that it is capable of further modifications, uses and/or adaptations of the invention following in general the principle of the invention, and including such departures from the present disclosure as those come within the known or customary practice in the art to which the invention pertains, and as may be applied to the central features hereinbefore set forth, and fall within the scope of the invention and of the limits of the claims appended hereto or presented later. The invention, therefore, is not limited to the preferred embodiment(s) shown/described herein.

REFERENCES

The following references, and any cited in the disclosure herein, are hereby incorporated herein in their entirety by reference.

1. Hansen, A., Childress, D., Miff, S., Gard, S., Mesplay, K. (2004) The Human Ankle During Walking: Implications for Design of Biomimetic Ankle Prostheses and Orthoses. Journal of Biomechanics, Vol. 37, No. 10, 1467-1474.

2. Williams R J, Hansen A H, Gard S A. (2009) Prosthetic Ankle-Foot Mechanism Capable of Automatic Adaptation to the Walking Surface. Journal of Biomechanical Engineering, Vol., 131, No. 3, 035002.

3. Hansen A, Brielmaier S, Medvec J, Pike A, Nickel E, Merchak P, Weber M (2012) Prosthetic Foot with Adjustable Stability and its Effects on Balance and Mobility. 38th Annual Meeting and Scientific Symposium of the American Academy of Orthotists and Prosthetists, March 21-24, Atlanta. Ga.

4. Nickel E A, Hansen A H, Gard S A. (2012) Prosthetic Ankle-Foot System that Adapts to Sloped Surfaces. ASME Journal of Medical Devices, Vol. 6, No. 1, 011006. 

What is claimed is:
 1. An ankle-foot prosthesis, comprising: a) a foot plate including a rear portion and a forward deflectable portion; b) an ankle frame including anterior and posterior portions and an apex portion; c) said posterior portion of said ankle frame attached to said rear portion of said foot plate; d) a yoke including front and rear end portions, and a fulcrum point therebetween; e) said yoke pivotally connected to said apex portion of said ankle frame at the fulcrum point thereof and including a member for attaching to a prosthetic leg; f) a hydraulic damper having a first end pivotally connected to the rear end portion of said yoke and a second end pivotally connected to said ankle frame; g) a stiffness member disposed in parallel to said damper; h) a fluid control circuit for controlling extension and compression of said damper; i) said anterior portion of said ankle frame including a curved surface inclined upwardly relative to said foot plate and forwardly toward said forward deflectable portion of said foot plate; and j) said curved surface forming a roll-over surface for limiting a dorsiflexion deflection of said forward deflectable portion of said foot plate by a direct engagement therewith.
 2. The ankle-foot prosthesis of claim 1, wherein: a) said fluid control circuit includes a cutoff valve for allowing dorsiflexion and plantarflexion of said ankle-foot prosthesis.
 3. The ankle-foot prosthesis of claim 2, wherein: a) said cutoff valve allows movement of said ankle-foot prosthesis during a gait cycle between prosthetic side toe off and the next prosthetic side foot flat.
 4. The ankle-foot prosthesis of claim 2, wherein: a) said cutoff valve allows extension of said damper during a gait cycle at least between prosthetic side toe off and 0 to 0.13 seconds thereafter.
 5. The ankle-foot prosthesis of claim 1, further comprising: a) at least one check valve for said fluid control circuit for allowing compression of said damper.
 6. The ankle-foot prosthesis of claim 1, further comprising: a) at least one variable fluid-flow resistor for said fluid control circuit for adjusting hydraulic fluid resistance in dorsiflexion, plantarflexion, or both.
 7. The ankle-foot prosthesis of claim 1, wherein: a) said stiffness member comprises a spring or an elastic member.
 8. The ankle-foot prosthesis of claim 1, wherein: a) said spring comprises at least one of a compression spring, an extension spring, a compression tube spring, an extension tube spring, and a curved leaf spring.
 9. The ankle-foot prosthesis of claim 1, further comprising first and second check valves for said fluid control circuit, said first check valve arranged in parallel with said second check valve, said first check valve for allowing compression of said damper, said second check valve for allowing extension of said damper.
 10. The ankle-foot prosthesis of claim 1, further comprising first and second cutoff valves for said fluid control circuit, said first cutoff valve arranged in parallel with said second cutoff valve, said first cutoff valve for allowing plantarflexion of said ankle-foot prosthesis, said second cutoff valve for allowing dorsiflexion of said ankle-foot prosthesis.
 11. The ankle-foot prosthesis of claim 1, further comprising first and second variable fluid-flow resistors for said fluid control circuit, said first variable fluid-flow resistor arranged in parallel with said second variable fluid-flow resistor, said first variable fluid-flow resistor for adjusting hydraulic fluid resistance in plantarflexion, said second variable fluid-flow resistor for adjusting hydraulic fluid resistance in dorsiflexion.
 12. The ankle-foot prosthesis of claim 1, further comprising at least one variable fluid-flow resistor for said fluid control circuit, said at least one variable fluid-flow resistor for adjusting fluid resistance in plantarflexion.
 13. The ankle-foot prosthesis of claim 2, further comprising first and second check valves for said fluid control circuit, said first check valve arranged in parallel with said second check valve, said first check valve for allowing compression of said damper, said second check valve for allowing extension of said damper.
 14. The ankle-foot prosthesis of claim 2, further comprising: at least one variable fluid-flow resistor for said fluid control circuit for adjusting hydraulic fluid resistance in plantarflexion; and first and second check valves for said fluid control circuit, said first check valve arranged in parallel with said second check valve, said first check valve for allowing compression of said damper, said second check valve for allowing extension of said damper.
 15. The ankle-foot prosthesis of claim 2, further comprising: first and second check valves for said fluid control circuit, said first check valve arranged in parallel with said second check valve, said first check valve for allowing compression of said damper, said second check valve for allowing extension of said damper; and first and second variable fluid-flow resistors for said fluid control circuit, said first variable fluid-flow resistor arranged in parallel with said second variable fluid-flow resistor, said first variable fluid-flow resistor for adjusting hydraulic fluid resistance in plantarflexion, said second variable fluid-flow resistor for adjusting hydraulic fluid resistance in dorsiflexion.
 16. The ankle-foot prosthesis of claim 5, further comprising a cutoff valve for said fluid control circuit for allowing dorsiflexion of said ankle-foot prosthesis.
 17. The ankle-foot prosthesis of claim 6, further comprising: first and second check valves for said fluid control circuit, said first check valve arranged in parallel with said second check valve, said first check valve for allowing compression of said damper, said second check valve for allowing extension of said damper; and a cutoff value for said fluid control circuit for allowing dorsiflexion of said ankle-foot prosthesis.
 18. The ankle-foot prosthesis of claim 9, further comprising first and second cutoff valves for said fluid control circuit, said first cutoff valve arranged in parallel with said second cutoff valve, said first cutoff valve for allowing plantarflexion of said ankle-foot prosthesis, said second cutoff valve for allowing dorsiflexion of said ankle-foot prosthesis.
 19. The ankle-foot prosthesis of claim 9, further comprising: first and second variable fluid-flow resistors for said fluid control circuit, said first variable fluid-flow resistor arranged in parallel with said second variable fluid-flow resistor, said first variable fluid-flow resistor for adjusting hydraulic fluid resistance in plantarflexion, said second variable fluid-flow resistor for adjusting hydraulic fluid resistance in dorsiflexion; and a cutoff valve for said fluid control circuit for allowing dorsiflexion of said ankle-foot prosthesis.
 20. The ankle-foot prosthesis of claim 9, further comprising: first and second cutoff valves for said fluid control circuit, said first cutoff valve arranged in parallel with said second cutoff valve, said first cutoff valve for allowing plantarflexion of said ankle-foot prosthesis, said second cutoff valve for allowing dorsiflexion of said ankle-foot prosthesis; and first and second variable fluid-flow resistors for said fluid control circuit, said first variable fluid-flow resistor arranged in parallel with said second variable fluid-flow resistor, said first variable fluid-flow resistor for adjusting hydraulic fluid resistance in plantarflexion, said second variable fluid-flow resistor for adjusting hydraulic fluid resistance in dorsiflexion.
 21. The ankle-foot prosthesis of claim 12, further comprising: first and second check valves for said fluid control circuit, said first check valve arranged in parallel with said second check valve, said first check valve for allowing compression of said damper, said second check valve for allowing extension of said damper; and first and second cutoff valves for said fluid control circuit, said first cutoff valve arranged in parallel with said second cutoff valve, said first cutoff valve for allowing plantarflexion of said ankle-foot prosthesis, said second cutoff valve for allowing dorsiflexion of said ankle-foot prosthesis. 